Design and synthesis of functional latex/silica nanocomposite films via colloidal self-assembly

The utilisation of self-stratification in binary and polydisperse colloidal dispersions shows great promise for the production of multi-layered functional coatings using only a single step process. Here, stratification is achieved in latex dispersions containing silica nanoparticles for a range of drying conditions. The resulting films possess enhanced hardness, and the variation in surface microstructure has a significant effect on the wettability of the surfaces. However, it was demonstrated that the silica enriched surface had poor abrasion resistance due to the hardness of the nanoparticles and their lack of cohesion within the films. This was overcome by the incorporation of additional smaller latex particles in a novel demonstration of the experimental drying of ternary colloidal dispersions. Furthermore, the ternary films retain the surface morphology, hardness, and wettability of the binary latex/silica coatings.

This thesis also explores the effects of particle interactions on colloidal stratification, and the differing morphologies and architectures which may arise as a result of changing particle interactions. Theories are presented for the formation of holey superstructures as a result of electrostatic repulsions between particles. These ideas are tested experimentally by introducing cationic surfactants to control the particle surface charges and alter the particle interactions during drying. This is further vindicated through the use of Brownian dynamics simulations.

The addition of surfactants is also shown to be a simple and effective method for inhibiting stratification, producing armoured particles, and controlling the transparency of colloidal coatings.

The final section of this project details the polymerisation of CO2-responsive DEAEMA and subsequent grafting onto silica nanoparticles. The modified particles are shown to have switchable stability in response to carbonation of water. While the resulting particle size made previous stratification mechanisms infeasible, the modification does allow the production of silica coatings through a simple casting technique which is usually unsuccessful due to the hard nature of the silica. The resulting surfaces also prove to have enhanced stability during immersion in water and are shown to be amphiphilic.

Overall, this thesis builds further on the understanding of colloidal stratification, in particular in relation to diffusiophoresis and particle interactions, showing how film architectures can be altered and controlled. The results also build towards the practical use of stratification to produce multi-layered functional coatings by showing how mechanical properties can be enhanced through the single-step casting of water-based dispersions.